The energy needs of society are constantly growing. Techniques to meet this growing energy demand are continually sought after. One area of focus has been in the area of solar power. Solar power technology can take various forms. One technique is to use photovoltaic technology to convert light into electrical current. Another technique is called concentrating solar power or CSP.
Generally speaking, CSP uses mirrors to focus the radiation from the sun into a small area. This small area may be, for instance, a tower in the middle of a field of mirrors. The concentrated heat formed at the focal point (e.g., at the tower) may then be used to as a heat source in a conventional power plant (e.g., to run a turbine that creates electrical current), or for any other thermal application such as, for example, sea water desalination. Concentrated energy from mirrors may also be used to focus on photovoltaic cells to potentially increase their output.
Various types of mirrors may be used in CSP applications. Parabolic mirrors, for instance, are structured to focus a broad beam of light (e.g., light from the sun) into a single point. However, parabolic mirrors can be difficult and/or expensive to produce and maintain. Another type of mirror that may be used in CSP applications is a flat mirror. These mirrors sometimes have an advantage of being cheaper and easier to maintain than their parabolic counterparts.
The overall efficiency of a CSP application may relate to how efficiently the power plant captures the energy from the sun's radiation. One technique to improve the efficiency CSP applications may be to employ tracking technology that facilitates optimal positioning of the CSP mirrors in relation to the position of the sun in the sky (e.g., the mirrors may track the sun as the sun progress across the sky).
Another factor in the efficiency of CSP applications may be the reflective efficiency of the mirrors. Mirrors with higher reflectance rates will increase the overall efficiency of CSP applications. Accordingly, high reflectance mirrors are continually sought after in order to improve the efficiency of CSP applications.
One challenge lies in how to protect these mirrors from the environments in which they are located, which often are quite harsh. Indeed, it will be appreciated that CSP applications may be placed in harsh environments that may be subject to high wind loads and/or other conditions. A large piece of glass exposed to high winds may have a large amount of force directed to the exposed surface area of the glass substrate. The strength of the glass has been found to be generally proportional to the square of its thickness. Accordingly, if the wind force applied to the surface of the glass exceeds the structural strength of the glass the glass (and mirror) may break.
A broken mirror may have several additional negative consequences. First, the broken glass of the mirror may present a safety hazard to people working with the mirror (e.g., because of the shards of glass). Second, a painted backing layer may contain a certain percentage of lead in it. This lead concentration may make disposal of the now-broken mirror a hazardous process. Third, as the structural integrity for the mirror as a whole may be substantially dependent on the structural integrity of the glass substrate, a loss in the glass substrate's structural integrity (e.g., because of breaking) may be substantially carried over to the mirror as a whole. Thus, when a glass substrate breaks, the entire glass surface may be completely destroyed and potentially resulting in a complete loss of the mirror and its reflective functionality.
Thus, it will be appreciated the structural strength of the mirror may need to be sufficient to prevent breakage, especially in high wind environments.
To overcome structural stability issues, some mirrors have sometimes included relatively thick glass substrates. Unfortunately, however, the use of thicker glass substrates can negatively affect the performance of the mirror, e.g., as a result of higher absorption, reduced reflectance from the mirror, etc. Even very high transmission glass likely will not transmit 100% of the light impinging on it. Thus, some light will not reach the mirror coating on the back side of the glass, and some of the light reflected from the mirror coating on the back side of the glass will not be transmitted back out of the glass. Thus, increasing the thickness of the glass used on the mirror may lead to reduced reflectance rates and, ultimately, reduced efficiency in CSP applications. Additionally, the conventional technique of increasing the structural strength in mirrors by increasing the thickness of the glass substrate also increases the cost of entire assembly, e.g., as a result of high material costs because high transmission low iron solar glass types are typically of higher cost than regular glass.
One or more layers of paint may be provided to conventional mirrors, e.g., to help protect the layered coating from the environment. Unfortunately, however, the applied paint may still be susceptible to UV radiation. Accordingly, in order to protect the paint from UV radiation the thickness of the silver coating in the layered coating may be increased in order to provide sufficient protection. As will be appreciated, this extra thickness of silver may further increase the cost of a mirror.
Thus, it will be appreciated that techniques for increasing (or maintaining) the durability of mirrors in CSP application while also maintaining (or increasing) a mirrors reflectance percentage are continuously sought after. It also will be appreciated that there exists a need in the art for improved mirrors and the like that, for example, can be used in CSP applications.
Certain example embodiments of this invention relate to a method of making an article. A first low-iron glass substrate is provided, with the first substrate having a thickness of about 0.5-3 mm. A reflective coating is disposed on a major surface of the first substrate. A radiation curable laminating adhesive is disposed over the reflective coating. A second glass substrate is provided substantially parallel to the first substrate, with the second substrate being oriented over the radiation curable laminating adhesive. The substrates is irradiated such that radiation causes the adhesive to become a solid polymer interlayer to laminate together the first substrate with the reflective coating disposed thereon and the second substrate to form a reflective article. The reflective article has a reflectivity of at least 90 percent.
Certain example embodiments of this invention relate to a method of making an article. A first low-iron glass substrate is provided, with the first substrate having a thickness of about 0.5-3 mm. A multi-layer thin-film reflective coating is disposed on a major surface of the first substrate. The reflective coating comprises, in order moving away from the substrate, a tin-inclusive layer, an Ag-inclusive layer directly contacting the tin-inclusive layer, and a copper-inclusive layer directly contacting the Ag-inclusive layer. A radiation curable laminating adhesive is disposed over the reflective coating. A second glass substrate is substantially parallel to the first substrate, with the second substrate being oriented over the laminating adhesive, and with the second substrate being at least as thick as the first substrate. The second substrate has an iron content higher than an iron content of the first substrate. The first substrate with the reflective coating disposed thereon and the second substrate are laminated together to form a reflective article by irradiating the substrates with UV radiation such that the radiation curable laminating adhesive is cured to form a solid polymer interlayer.
Certain example embodiments of this invention relate to a coated article. A first low-iron glass substrate has a thickness of 0.5-3 mm. A reflective coating comprises a plurality of thin film layers disposed on a major surface of the first substrate. A second substrate is substantially parallel to the first high transmission substrate, with the second substrate having a higher iron content than the first substrate and being at least twice as thick as the first substrate. The first and second substrates are laminated together with a radiation cured polymer interlayer. The polymer interlayer hermetically seals the reflective coating between the first and second substrates. The reflective article has a reflectivity above 90 percent.
The features, aspects, advantages, and example embodiments described herein may be combined in any suitable combination or sub-combination to realize yet further embodiments.